Ink jet printing apparatus produce a plurality of uniform drops aligned parallel to one another and perpendicular to the movement of paper or other material upon which printing is to be effected. The printing is produced by using a reservoir of printing fluid (herein referred to as ink, but which can have varying compositions as is well known in the art) with a plurality of parallel aligned orifices at the bottom of the reservoir through which the fluid is ejected or permitted to flow at a predetermined rate and in such a manner as to produce drops of fluid at the ends of the filaments of the ink which pass through the orifices. These drops are then selectively charged or not charged as they pass through holes in a charge plate and are subsequently caught in a catcher or deposited on the material which is being printed.
A popular type of ink jet printing apparatus employs a relatively thick and rigid orifice plate. A vibrating plate positioned above the liquid reservoir creates a uniform pressure on the printing fluid and forces it through the orifice plate. Such apparatus is disclosed in U.S. Pat. No. 3,900,162.
The design specifications for such orifice plates are demanding and difficult to meet. Specifically, to provide acceptable quality printing, the orifices must be aligned in a rigorously straight line with the centers of the orifices being spaced equidistant from each other. In addition, the rate of fluid flow through each orifice must be essentially the same.
Economical methods of forming the orifices in the orifice plate are difficult to find since the nature of the system requires the use of extremely small diameter holes in these plates. For example, the orifices in the orifice plate are generally in the range of 0.0005-0.0015 inch in diameter. In the past, this has required very expensive, time consuming and exotic methods of manufacturing orifice plates having uniform diameter orifices.
One method for preparing such orifice plates involves first encapsulating a plurality of parallel glass capillaries in a block of epoxy resin, solder glass, or the like. Plates of the desired thickness then are made by making orthogonal cuts across the axes of the capillaries. Such a method is disclosed in the Cone patent U.S. Pat. No. 4,112,436. In preparing orifice plates from glass capillaries, it is difficult to obtain a reliable supply of capillaries having orifices of uniform diameter throughout their length. As a consequence, a significant percentage of the orifice plates do not have sufficiently uniform fluid flow rates through each orifice to be acceptable for use.
Accordingly, there is a need in the art for an improved and economical method for preparing orifice plates whose orifices provide very uniform fluid flow rates.